Lithium-ion secondary battery

Abstract

This lithium ion secondary battery (1) comprises: a negative electrode (12); a positive electrode (10); a nonaqueous electrolyte (18) including a lithium salt; an aqueous electrolyte (16) including a lithium salt; and a partition wall layer (14) disposed between the negative electrode (12) and the positive electrode (10). The aqueous electrolyte (16) is in contact with the positive electrode (10), and the nonaqueous electrolyte (18) is in contact with the negative electrode (12). The partition wall layer (14) includes a nonaqueous solid electrolyte in which a matrix polymer and a nonaqueous electrolytic solution are formed into a complex. The matrix polymer includes a copolymer of acrylonitrile and at least one of methyl methacrylate, methyl acrylate, and vinyl acetate.

Description

[Technical Field]

[0001] The present disclosure relates to lithium-ion secondary batteries. [Background technology]

[0002] Lithium-ion secondary batteries, which have a positive electrode, a negative electrode, and an electrolyte, are widely used as high-power, high-energy-density secondary batteries. Conventional secondary batteries use organic solvent-based electrolytes to achieve high energy density.

[0003] However, organic solvents are generally flammable, making safety an important issue, and the ionic conductivity of organic solvents is lower than that of aqueous solutions, making rapid charge / discharge characteristics insufficient.

[0004] In view of these problems, secondary batteries using aqueous electrolytes containing water have been studied (e.g., Patent Documents 1 to 4). For example, Patent Document 1 proposes a lithium ion secondary battery that uses an aqueous solution containing a high concentration of alkaline salt as the aqueous liquid electrolyte. Furthermore, Patent Document 2 proposes a lithium ion secondary battery that includes a negative electrode filled with a nonaqueous solid electrolyte, a positive electrode, a separator disposed between the negative electrode and the positive electrode and filled with the nonaqueous solid electrolyte, and an aqueous liquid electrolyte.

[0005] Non-Patent Document 1 discloses a method for producing a non-porous membrane of a solid electrolyte by a phase inversion method using a poor solvent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6423453 [Patent Document 2] Japanese Patent Application Publication No. 2018-198131 [Patent Document 3] Japanese Patent Application Laid-Open No. 2018-156895 [Patent Document 4] Japanese Patent Application Publication No. 2018-156837 [Non-patent literature]

[0007] [Non-Patent Document 1] Electrochimica Acta 49,(2004), 3339-3345 Summary of the Invention [Problem to be solved by the invention]

[0008] However, conventional lithium ion secondary batteries with aqueous electrolytes have a problem of capacity reduction due to charge / discharge cycles.

[0009] Therefore, an object of the present disclosure is to provide a lithium ion secondary battery that uses an aqueous electrolyte but is capable of suppressing a decrease in capacity due to charge / discharge cycles. [Means for solving the problem]

[0010] One aspect of the present disclosure is a lithium-ion secondary battery including a negative electrode, a positive electrode, a nonaqueous electrolyte containing a lithium salt, an aqueous electrolyte containing a lithium salt, and a partition layer disposed between the negative electrode and the positive electrode, wherein the aqueous electrolyte is in contact with only the positive electrode of the negative electrode and the positive electrode, and the nonaqueous electrolyte is in contact with at least the negative electrode of the negative electrode and the positive electrode, the partition layer includes a nonaqueous solid electrolyte A formed by combining a matrix polymer and a nonaqueous electrolytic solution, and the matrix polymer includes a copolymer of acrylonitrile and at least one of methyl methacrylate, methyl acrylate, and vinyl acetate. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a lithium ion secondary battery capable of suppressing a decrease in capacity due to charge / discharge cycles. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another example of the lithium ion secondary battery of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] A lithium-ion secondary battery according to one embodiment of the present disclosure includes a negative electrode, a positive electrode, a nonaqueous electrolyte containing a lithium salt, an aqueous electrolyte containing a lithium salt, and a partition layer disposed between the negative electrode and the positive electrode. The aqueous electrolyte is in contact with only the positive electrode of the negative electrode and the positive electrode, and the nonaqueous electrolyte is in contact with at least the negative electrode of the negative electrode and the positive electrode. The partition layer includes a nonaqueous solid electrolyte A formed by combining a matrix polymer and a nonaqueous electrolytic solution. The matrix polymer includes a copolymer of acrylonitrile with at least one of methyl methacrylate, methyl acrylate, and vinyl acetate. The use of a lithium-ion secondary battery according to one embodiment of the present disclosure can suppress capacity loss associated with charge-discharge cycles. While the mechanism behind this effect is not fully understood, the following is presumed.

[0014] By contacting the aqueous electrolyte only with the positive electrode, water side reactions at the negative electrode are suppressed, allowing charge-discharge reactions to proceed. However, if water in the aqueous electrolyte on the positive electrode side migrates over time through the partition layer between the positive electrode and the negative electrode to the negative electrode side, water side reactions occur, making it more likely that capacity will decrease with charge-discharge cycles. However, as disclosed herein, by using a partition layer containing a nonaqueous solid electrolyte A in which a matrix polymer and a nonaqueous electrolyte solution are composited, and the matrix polymer contains a copolymer of acrylonitrile with at least one of methyl methacrylate, methyl acrylate, and vinyl acetate, water in the aqueous electrolyte on the positive electrode side is prevented from migrating to the negative electrode side, thereby suppressing water side reactions and ultimately suppressing capacity loss with charge-discharge cycles.

[0015] An example of an embodiment of a lithium ion secondary battery according to the present disclosure will be described in detail below.

[0016] Fig. 1 is a schematic cross-sectional view showing an example of a lithium-ion secondary battery according to the present embodiment. The lithium-ion secondary battery 1 shown in Fig. 1 includes a positive electrode 10, a negative electrode 12, a partition layer 14, an aqueous electrolyte 16, a non-aqueous electrolyte 18, a positive electrode lead 20, a negative electrode lead 22, and a battery case 24 that houses these components.

[0017] The positive electrode 10 has a positive electrode current collector 26 and a positive electrode composite layer 28 disposed on the positive electrode current collector 26. A positive electrode lead 20 is connected to the positive electrode current collector 26. The positive electrode lead 20 is housed in the battery case 24 such that the tip of the positive electrode lead 20 protrudes outside the battery case 24.

[0018] The negative electrode 12 has a negative electrode current collector 30 and a negative electrode composite layer 32 disposed on the negative electrode current collector 30. A negative electrode lead 22 is connected to the negative electrode current collector 30. The negative electrode lead 22 is housed in the battery case 24 such that the tip of the negative electrode lead 22 protrudes outside the battery case 24.

[0019] The aqueous electrolyte 16 is, for example, impregnated into the positive electrode mixture layer 28 and is in contact with only the positive electrode 10 out of the positive electrode 10 and the negative electrode 12. The nonaqueous electrolyte 18 is, for example, impregnated into the negative electrode mixture layer 32 and is in contact with the negative electrode 12. The nonaqueous electrolyte 18 may be in contact with only the negative electrode 12 out of the positive electrode 10 and the negative electrode 12, or may be in contact with both the positive electrode 10 and the negative electrode 12. The partition wall layer 14 is disposed between the positive electrode 11 and the negative electrode 12. The partition wall layer 14 may be wrapped around the negative electrode 12.

[0020] <Positive electrode 10> The positive electrode current collector 26 may be a foil of a metal that is electrochemically and chemically stable within the potential range of the positive electrode 10, or a film having such a metal disposed on its surface. The form of the positive electrode current collector 26 is not particularly limited, and may be, for example, a porous body such as a mesh body, punched sheet, or expanded metal of the metal. Examples of materials for the positive electrode current collector 26 include stainless steel, Al, aluminum alloy, and Ti. From the viewpoints of current collection performance, mechanical strength, and the like, the thickness of the positive electrode current collector 26 is preferably, for example, 3 μm or more and 50 μm or less.

[0021] Positive electrode mixture layer 28 includes a positive electrode active material. Positive electrode mixture layer 28 may also include a binder, a conductive material, etc. Positive electrode 10 can be manufactured, for example, by applying a positive electrode mixture slurry including a positive electrode active material, a binder, a conductive material, etc., onto positive electrode current collector 26, drying and rolling the coating, and forming positive electrode mixture layer 28 on positive electrode current collector 26.

[0022] Examples of the positive electrode active material include lithium-containing transition metal oxides containing lithium (Li) and transition metal elements such as cobalt (Co), manganese (Mn), and nickel (Ni). Other examples of the positive electrode active material include transition metal sulfides, metal oxides, lithium-containing polyanion compounds containing one or more transition metals such as lithium iron phosphate (LiFePO) and lithium iron pyrophosphate (LiFePO), sulfur-based compounds (LiS), and oxygen-containing metal salts such as oxygen and lithium oxide. For example, from the viewpoint of charge / discharge efficiency, lithium-containing transition metal oxides are preferred as the positive electrode active material.

[0023] From the viewpoint of, for example, charge / discharge efficiency, the lithium-containing transition metal oxide preferably contains at least one element selected from the group consisting of Ni, Co, Mn, and aluminum (Al). Among these elements, it is preferable to contain at least Ni, at least Co, at least two elements of Ni and Mn, at least three elements of Ni, Co, and Mn, or at least three elements of Ni, Co, and Al. The lithium-containing transition metal oxide may contain additional elements other than these elements, such as zirconium (Zr), boron (B), magnesium (Mg), scandium (Sc), yttrium (Y), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), lead (Pb), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb), and silicon (Si).

[0024] Specific examples of lithium-containing transition metal oxides include Li x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z , Li x Ni 1-y M y O z , Li x Mn2O4, Li x Mn 2-y M yO4, LiMPO4, Li2MPO4F (in each chemical formula, M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3) can be mentioned. The lithium-containing transition metal oxide may be used alone or in combination of multiple kinds. From the viewpoint of increasing the capacity, it is preferable that the lithium-containing transition metal oxide contains 80 mol% or more of Ni with respect to the total amount of transition metals other than lithium. Also, from the viewpoint of the stability of the crystal structure, the lithium-containing transition metal oxide is Li a Ni b Co c Al d O2 (0 < a ≤ 1.2, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d ≤ 0.1, b + c + d = 1) is more preferable.

[0025] In addition, the lithium-containing transition metal oxide may be a Li-excess type transition metal oxide, a lithium-containing transition metal halogen oxide, etc. The Li-excess type transition metal oxide is represented by, for example, the general formula Li 1+x Me 1-x O2 (0 < x). Also, the lithium-containing transition metal halogen oxide is not particularly limited as long as it is a lithium-containing transition metal oxide containing a halogen atom. However, for example, from the viewpoint of the structural stability of the lithium-containing transition metal oxide, etc., it is preferable to include a lithium-containing transition metal oxide containing a fluorine atom.

[0026] The conductive material may be a known conductive material that enhances the electrical conductivity of the positive electrode mixture layer 28, such as carbon black, acetylene black, ketjen black, graphite, carbon nanofibers, carbon nanotubes, graphene, or other carbon materials. The binder may be a known binder that maintains good contact between the positive electrode active material and the conductive material and enhances the binding of the positive electrode active material to the surface of the positive electrode current collector 26, such as fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, carboxymethyl cellulose (CMC) or a salt thereof, styrene-butadiene rubber (SBR), polyethylene oxide (PEO), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP).

[0027] <Negative electrode 12> The negative electrode current collector 30 may be a foil of a metal that is electrochemically and chemically stable within the potential range of the negative electrode 12, or a film having such a metal disposed on its surface. The form of the negative electrode current collector 30 is not particularly limited, and may be, for example, a porous body such as a mesh, punched sheet, or expanded metal. Examples of materials for the negative electrode current collector 30 include Al, Ti, Mg, Zn, Pb, Sn, Zr, and In. These may be used alone or as an alloy of two or more elements, as long as the material contains at least one of them as a main component. Furthermore, when two or more elements are contained, the elements do not necessarily need to be alloyed. The thickness of the negative electrode current collector 30 is preferably, for example, 3 μm to 50 μm inclusive, from the viewpoints of current collection performance, mechanical strength, and the like.

[0028] The negative electrode mixture layer 32 contains a negative electrode active material. The negative electrode mixture layer 32 may also contain a binder, a conductive material, a thickener, and the like. The conductive material and binder may be the same as those used for the positive electrode 10. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, a conductive material, and the like onto the negative electrode current collector 30, drying and rolling the coating, and forming the negative electrode mixture layer 32 on the negative electrode current collector 30.

[0029] Examples of thickeners include carboxymethyl cellulose (CMC) and its modified products (including salts such as Na salt), cellulose derivatives such as methyl cellulose (cellulose ethers, etc.), saponified polymers having vinyl acetate units such as polyvinyl alcohol, polyethers (polyalkylene oxides such as polyethylene oxide, etc.), etc. These may be used alone or in combination of two or more.

[0030] The negative electrode active material is not particularly limited as long as it is a material that can be used as a negative electrode active material in conventional lithium-ion secondary batteries. Examples include carbon materials such as artificial graphite, natural graphite, hard carbon, soft carbon, carbon nanotubes, and activated carbon; metals such as Li, Si, and Sn, and their alloys, oxides, metal sulfides, and metal nitrides. Examples of Li alloys include lithium aluminum alloys, lithium tin alloys, lithium lead alloys, and lithium silicon alloys. Examples of metal oxides containing Li include lithium titanate (Li4Ti5O 12 Examples of metal nitrides containing Li include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. Further examples include sulfur-based compounds.

[0031] Generally, in a lithium ion secondary battery using an aqueous electrolyte, when a carbon material is used as a negative electrode active material, the side reaction of water has a large effect, and the battery capacity decreases significantly with charge-discharge cycles. However, in the lithium ion secondary battery of this embodiment, as described above, contact of water with the negative electrode is suppressed, so that even when a carbon material is used as a negative electrode active material, it is possible to suppress the decrease in capacity with charge-discharge cycles.

[0032] <Aqueous electrolyte 16> The aqueous electrolyte 16 contains a lithium salt. The aqueous electrolyte 16 containing a lithium salt is, for example, an aqueous liquid electrolyte containing a lithium salt and an aqueous solvent, or an aqueous solid electrolyte in which a lithium salt, an aqueous solvent, and a matrix polymer are combined. The aqueous solid electrolyte can be obtained, for example, by dissolving a lithium salt in an aqueous solvent, and then drying a precursor solution in which a matrix polymer is mixed or dissolved. The aqueous electrolyte 16 may be liquid or solid, but is preferably an aqueous liquid electrolyte in terms of further improving battery characteristics.

[0033] The aqueous solvent is a solvent containing water, and may be water alone or may contain water and a solvent other than water. The water content relative to the total amount of the aqueous solvent is preferably 50% or more by volume, for example, from the viewpoint of improving the safety of the lithium-ion secondary battery 1.

[0034] Furthermore, the amount of water relative to the lithium salt contained in the aqueous electrolyte 16 is preferably 1:4 or less, more preferably in the range of 1:0.5 to 1:4, and even more preferably in the range of 1:0.5 to 1:3, in terms of the molar ratio of lithium salt to water. When the amount of water relative to the lithium salt contained in the aqueous electrolyte 16 is within the above range, the potential window of the aqueous electrolyte 16 may be expanded, for example, compared to when the amount is outside the above range, and the voltage applied to the lithium-ion secondary battery 1 may be increased.

[0035] Examples of solvents other than water contained in the aqueous solvent include organic solvents such as esters, ethers, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. Furthermore, halogen-substituted solvents in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine may also be used. Specifically, from the viewpoint of improving the battery characteristics of the lithium-ion secondary battery 1, preferred are, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylidene carbonate, and butylene carbonate; linear carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; and fluorinated carbonates containing fluorine as a constituent element such as fluoroethylene carbonate, fluorodimethyl carbonate, and methyl fluoropropionate. Among the above-listed solvents, cyclic carbonates and fluorinated carbonates containing fluorine as a constituent element are particularly preferred, for example, from the viewpoint of suppressing self-discharge of the battery. Furthermore, among the above-listed fluorinated carbonates, fluoroethylene carbonate is preferred. These organic solvents may be used alone or in combination of two or more.

[0036] The amount of organic solvent relative to the lithium salt contained in the aqueous electrolyte 16, expressed as a molar ratio of lithium salt:organic solvent, is preferably in the range of 1:0 to 1:2.5, and more preferably in the range of 1:0 to 1:2. When the amount of organic solvent relative to the lithium salt is within this range, the battery characteristics of the lithium ion secondary battery may be improved compared to when the amount is outside this range.

[0037] Any lithium salt can be used as long as it dissolves in an aqueous solvent and dissociates, causing lithium ions to exist in the aqueous electrolyte 16. Examples of such lithium salts include salts with inorganic acids such as perchloric acid, sulfuric acid, and nitric acid, salts with halide ions such as chloride ions and bromide ions, and salts with organic anions containing carbon atoms in the structure.

[0038] Examples of organic anions constituting the lithium salt include anions represented by the following general formulas (i) to (vi). (R 1 SO2)(R 2 SO2)N - (i) (R 1 , R 2 are each independently selected from an alkyl group or a halogen-substituted alkyl group. 1 and R 2 may be bonded to each other to form a ring. R 3 SO3 - (ii) (R 3 is selected from alkyl groups or halogen-substituted alkyl groups. R 4 CO2 - (iii) (R 4 is selected from alkyl groups or halogen-substituted alkyl groups. (R 5 SO2)3C - (iv) (R 5 is selected from alkyl groups or halogen-substituted alkyl groups. [(R 6 SO2)N(SO2)N(R 7 SO2)] 2- (v) (R 6 , R 7 is selected from alkyl groups or halogen-substituted alkyl groups. [(R 8 SO2)N(CO)N(R 9 SO2)] 2- (vi) (R 8 , R 9 is selected from alkyl groups or halogen-substituted alkyl groups.

[0039] In the above general formulas (i) to (vi), the number of carbon atoms in the alkyl group or halogen-substituted alkyl group is preferably 1 to 6, more preferably 1 to 3, and even more preferably 1 or 2. The halogen in the halogen-substituted alkyl group is preferably fluorine. The number of halogen substitutions in the halogen-substituted alkyl group is equal to or less than the number of hydrogen atoms in the original alkyl group.

[0040] R 1 ~R 9 Each of the groups is, for example, a group represented by the following general formula (vii): C n H a F b Cl c Br d I e (vii) (n is an integer greater than or equal to 1, and a, b, c, d, and e are integers greater than or equal to 0, and satisfy 2n+1=a+b+c+d+e.)

[0041] Specific examples of the organic anion represented by the general formula (i) include bis(trifluoromethanesulfonyl)imide (TFSI; [N(CF3SO2)2] - ), bis(perfluoroethanesulfonyl)imide (BETI; [N(C2F5SO2)2] - ), (perfluoroethanesulfonyl)(trifluoromethanesulfonyl)imide ([N(C2F5SO2)(CF3SO2)] - ) and the like. Specific examples of the organic anion represented by the general formula (ii) include, for example, CF3SO3 - , C2F5SO3 - Specific examples of the organic anion represented by the general formula (iii) include CF3CO2 - , C2F5CO2 - Specific examples of the organic anion represented by the general formula (iv) include tris(trifluoromethanesulfonyl)carbonate ([(CF3SO2)3C] - ), tris(perfluoroethanesulfonyl)carbonate ([(C2F5SO2)3C] - ) and the like. Specific examples of the organic anion represented by the general formula (V) include sulfonylbis(trifluoromethanesulfonyl)imide ([(CF3SO2)N(SO2)N(CF3SO2)] 2- ), sulfonylbis(perfluoroethanesulfonyl)imide ([(C2F5SO2)N(SO2)N(C2F5SO2)] 2-), sulfonyl(perfluoroethanesulfonyl)(trifluoromethanesulfonyl)imide ([(C2F5SO2)N(SO2)N(CF3SO2)] 2- ) and the like. Specific examples of the organic anion represented by the general formula (vi) include carbonylbis(trifluoromethanesulfonyl)imide ([(CF3SO2)N(CO)N(CF3SO2)] 2- ), carbonylbis(perfluoroethanesulfonyl)imide ([(C2F5SO2)N(CO)N(C2F5SO2)] 2- ), carbonyl(perfluoroethanesulfonyl)(trifluoromethanesulfonyl)imide ([(C2F5SO2)N(CO)N(CF3SO2)] 2- ) etc.

[0042] Examples of organic anions other than those represented by the general formulae (i) to (vi) above include anions such as bis(1,2-benzenediolate(2-)-O,O')borate, bis(2,3-naphthalenediolate(2-)-O,O')borate, bis(2,2'-biphenyldiolate(2-)-O,O')borate, and bis(5-fluoro-2-oleate-1-benzenesulfonic acid-O,O')borate.

[0043] The anion constituting the lithium salt is preferably an imide anion. Specific examples of suitable imide anions include the imide anions exemplified as the organic anions represented by the general formula (i) above, as well as bis(fluorosulfonyl)imide (FSI; [N(FSO2)2] - ), (fluorosulfonyl)(trifluoromethanesulfonyl)imide (FTI; [N(FSO2)(CF3SO2)] - ) etc.

[0044] As the lithium salt having a lithium ion and an imide anion, for example, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethanesulfonyl)imide (LiBETI), lithium (perfluoroethanesulfonyl)(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide (LiFTI) are preferred, with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) being more preferred, in terms of being able to effectively suppress self-discharge of the battery. These may be used alone or in combination of two or more.

[0045] Specific examples of other lithium salts include CF3SO3Li, C2F5SO3Li, CF3CO2Li, C2F5CO2Li, (CF3SO2)3CLi, (C2F5SO2)3CLi, (C2F5SO2)2(CF3SO2)CLi, (C2F5SO2)(CF3SO2)2CLi, [(CF3SO2)N(SO2)N(CF3SO2)]Li2, [(C2F5SO2)N(SO2)N(C2F5SO2)]Li2, [(C2F5SO2)N(SO2)N(CF3SO2)]Li2, [(CF3SO2)N(CO)N(CF3SO2)]Li2, [(C2F5SO2)N (CO)N(CFSO)]Li, lithium bis(1,2-benzenediolate(2-)-O,O')borate, lithium bis(2,3-naphthalenediolate(2-)-O,O')borate, lithium bis(2,2'-biphenyldiolate(2-)-O,O')borate, lithium bis(5-fluoro-2-oleate-1-benzenesulfonic acid-O,O')borate, lithium perchlorate (LiClO), lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium nitrate (LiNO), lithium sulfate (LiSO), lithium sulfide (LiS), lithium hydroxide (LiOH), etc. These may be used alone or in combination of two or more.

[0046] The lithium salt contained in the aqueous electrolyte 16 preferably contains lithium ions and imide anions, for example, in order to improve the battery characteristics of the lithium ion secondary battery, and the concentration of the lithium salt in the aqueous electrolyte is preferably 4.5 mol / L to 6 mol / L.

[0047] When the aqueous electrolyte 16 is an aqueous solid electrolyte, examples of the matrix polymer contained therein include polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), etc. Alternatively, a polymer obtained by mixing monomers, acrylonitrile and acrylic acid, and thermally polymerizing them may be used.

[0048] The content of the matrix polymer is, for example, preferably 1% by mass or more and 15.0% by mass or less, and more preferably 3% by mass or more and 10% by mass or less, relative to the total amount of the aqueous electrolyte 16. By setting the content within this range, for example, gelation or solidification of the aqueous electrolyte 16 becomes easier.

[0049] When the aqueous electrolyte 16 is an aqueous solid electrolyte, the entire cathode 10 may be coated with the aqueous electrolyte, or at least the cathode mixture layer 28 may be coated with the aqueous electrolyte. The aqueous solid electrolyte can be obtained, for example, by dissolving a lithium salt in an aqueous solvent and further mixing or dissolving a matrix polymer in a precursor solution, applying the precursor solution to the cathode 10, or by immersing the cathode 10 in the precursor solution, coating the precursor solution on the cathode 10, and then drying the precursor solution. When the aqueous electrolyte 16 is an aqueous liquid electrolyte, the entire cathode 10 may be immersed in the aqueous liquid electrolyte, or the aqueous liquid electrolyte may simply be impregnated into the cathode mixture layer 28.

[0050] <Non-aqueous electrolyte 18> The nonaqueous electrolyte 18 contains a lithium salt. The nonaqueous electrolyte 18 containing a lithium salt is, for example, a nonaqueous liquid electrolyte containing a lithium salt and an organic solvent, or a nonaqueous solid electrolyte in which a lithium salt, an organic solvent, and a matrix polymer are combined. The nonaqueous solid electrolyte is prepared, for example, by dissolving a lithium salt in an organic solvent and then heating and drying a precursor solution in which a matrix polymer is further mixed or dissolved. The nonaqueous electrolyte 18 may be liquid or solid, but is preferably a nonaqueous liquid electrolyte in that it can further improve battery characteristics.

[0051] Examples of the organic solvent include known organic solvents used in conventional non-aqueous secondary batteries, such as the above-mentioned esters, ethers, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. Among these, it is preferable to use esters, ethers, nitriles, amides, and mixed solvents of two or more of these, in terms of improving battery characteristics.

[0052] Examples of esters include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; and carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone.

[0053] Examples of ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methylphenyl and chain ethers such as ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl.

[0054] The organic solvent preferably contains a halogen-substituted product in which hydrogen atoms of the above-mentioned various solvents are substituted with halogen atoms such as fluorine. Particularly preferred is at least one of fluorinated cyclic carbonates, fluorinated chain carbonates, and fluorinated ethers. Suitable examples of fluorinated cyclic carbonates include 4-fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, and 4,4,5,5-tetrafluoroethylene carbonate. Suitable examples of fluorinated chain carbonates include 2,2,2-ethyl trifluoroacetate, methyl 3,3,3-trifluoropropionate, and methyl pentafluoropropionate. Suitable examples of fluorinated ethers include 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0055] The organic solvent preferably contains a cyclic organic solvent such as a cyclic carbonate, for example, in order to suppress a decrease in the lithium ion conductivity of the non-aqueous electrolyte 18.

[0056] Examples of the lithium salt include known lithium salts used in conventional non-aqueous secondary batteries, such as LiPF, LiBF, LiAsF, LiClO, LiCF, SO, LiN(FSO), and LiN(ClF 2l+1 SO2)(C m F 2m+1 SO2) (l and m are integers of 1 or greater), LiC(C p F 2p+1 SO2)(C q F 2q+1 SO2)(C r F 2r+1 SO2) (p, q, and r are integers of 1 or greater), Li[B(C2O4)2] (lithium bis(oxalato)borate (LiBOB)), Li[B(C2O4)F2], Li[P(C2O4)F4], Li[P(C2O4)2F2], LiPO2F2, etc. The lithium salt may be, for example, the lithium salt used in the aqueous electrolyte 16, as exemplified above.

[0057] The matrix polymer may be the same as that used for the aqueous electrolyte 16. The content of the matrix polymer is, for example, preferably 1% by mass or more and 15.0% by mass or less, and more preferably 3% by mass or more and 10% by mass or less, relative to the total amount of the nonaqueous electrolyte 18. By setting the content within this range, for example, solidification of the nonaqueous electrolyte 18 becomes easier.

[0058] When the non-aqueous electrolyte 18 is a non-aqueous solid electrolyte, it is preferable that the non-aqueous electrolyte 18 has water repellency such that the solubility in 100 g of water at 25° C. is 2 g or less, for example, in order to effectively prevent contact between the negative electrode 12 and water. The water repellency of the non-aqueous electrolyte 18 can be increased, for example, by increasing the proportion of an organic solvent having a water-repellent substituent or a fluorinated organic solvent.

[0059] When the nonaqueous electrolyte 18 is a nonaqueous solid electrolyte, it may simply be coated on the surface of the negative electrode composite layer 32. However, because a side reaction with water also occurs on the negative electrode current collector 30 and the negative electrode lead 22, it is preferable that the entire negative electrode 12 be coated with the nonaqueous solid electrolyte, and more preferably, the negative electrode lead 22 (excluding the portion protruding from the battery case 24) be coated with the nonaqueous solid electrolyte. The nonaqueous solid electrolyte can be obtained, for example, by dissolving a lithium salt in an organic solvent and then coating or dissolving a matrix polymer in a precursor solution on the negative electrode 12, or by immersing the negative electrode 12 with the negative electrode lead 22 attached in the precursor solution, coating the negative electrode 12 with the precursor solution, and then drying the solution. When the nonaqueous electrolyte 18 is a nonaqueous liquid electrolyte, it is sufficient that the nonaqueous liquid electrolyte is impregnated into the negative electrode composite layer 32.

[0060] <Partition layer 14> The partition layer 14 contains a nonaqueous solid electrolyte A, which is a composite of a matrix polymer and a nonaqueous electrolyte solution. The matrix polymer contains a copolymer of acrylonitrile and at least one of methyl methacrylate, methyl acrylate, and vinyl acetate. The partition layer 14 is permeable to lithium ions and electrically separates the positive electrode 10 and the negative electrode 12. The partition layer 14 of this embodiment contains the nonaqueous solid electrolyte A, which suppresses water penetration and thus suppresses water migration from the positive electrode 10 to the negative electrode 12 through the partition layer 14. As a result, side reactions of water on the negative electrode 12 side are suppressed, and capacity loss due to charge / discharge cycles is suppressed.

[0061] The nonaqueous electrolyte solution may be any known nonaqueous electrolyte solution used in lithium ion secondary batteries, and may contain, for example, a lithium salt and a nonaqueous solvent. Examples of the lithium salt and nonaqueous solvent that can be used include those exemplified for the nonaqueous electrolyte 18 described above. From the viewpoint of lithium ion conductivity, the nonaqueous electrolyte solution preferably contains a cyclic organic solvent such as a cyclic carbonate ester. From the viewpoint of suppressing water permeability in the partition layer 14, the organic solvent preferably contains an organic solvent having a water-repellent substituent or a fluorinated organic solvent.

[0062] The matrix polymer may be any polymer containing a copolymer of acrylonitrile and at least one of methyl methacrylate, methyl acrylate, and vinyl acetate, but is preferably an acrylonitrile-methyl methacrylate copolymer, which can densify the nonaqueous solid electrolyte A and suppress water permeability in the partition layer 14. The content of the matrix polymer is preferably in the range of 5 mass % to 30 mass %, and more preferably in the range of 10 mass % to 25 mass %, relative to the total amount of the nonaqueous solid electrolyte A. By setting the content within this range, for example, the densification of the nonaqueous solid electrolyte A may be improved, and water permeability in the partition layer 14 may be further suppressed.

[0063] The non-aqueous solid electrolyte A can be obtained, for example, by a phase inversion method. An example of producing the non-aqueous solid electrolyte A by the phase inversion method will be described below. First, a solution is obtained by dissolving the matrix polymer in an organic solvent. The organic solvent is preferably a solvent in which the matrix polymer is easily soluble, such as dimethylformamide.

[0064] A solution containing a matrix polymer is applied to a substrate such as a glass plate or aluminum foil. A poor solvent (e.g., water) is then added to the coating on the substrate to solidify the matrix polymer and form a polymer skeleton (i.e., a polymer film). The polymer skeleton is then removed from the substrate and immersed in the poor solvent for a predetermined period of time, or dried by heat treatment such as vacuum heating.

[0065] The obtained polymer skeleton is immersed in a nonaqueous electrolyte solution for a predetermined time and then heated and dried for a predetermined time. This results in a membrane of nonaqueous solid electrolyte A, in which a matrix polymer consisting of the polymer skeleton and the nonaqueous electrolyte solution are combined. The obtained membrane of nonaqueous solid electrolyte A is in a gel or solid state. The produced membrane of nonaqueous solid electrolyte A is used as the partition layer 14.

[0066] The partition wall layer 14 containing the nonaqueous solid electrolyte A may be produced by a method other than the method using the phase inversion method. However, the method using the phase inversion method improves the density of the nonaqueous solid electrolyte A and can further suppress water permeability in the partition wall layer 14. As a production method other than the method using the phase inversion method, for example, a precursor solution obtained by mixing or dissolving a nonaqueous electrolytic solution and a matrix polymer in an organic solvent is applied to a porous sheet such as a separator and then dried. This results in the formation of the partition wall layer 14 in which the nonaqueous solid electrolyte A is coated on the porous sheet.

[0067] The thickness of the partition layer 14 may be, for example, in the range of 10 μm to 50 μm, or in the range of 15 μm to 30 μm.

[0068] The partition wall layer 14 is not limited to one composed only of the nonaqueous solid electrolyte A, and may also contain the nonaqueous solid electrolyte A and a nonaqueous solid electrolyte B composed of a component different from that of the nonaqueous solid electrolyte A. When the nonaqueous solid electrolytes A and B are contained, the partition wall layer 14 may be a single partition wall layer in which the nonaqueous solid electrolytes A and B are integrated, or may be a laminated structure in which a first partition wall layer containing the nonaqueous solid electrolyte A and a second partition wall layer containing the nonaqueous solid electrolyte B are laminated.

[0069] FIG. 2 is a schematic cross-sectional view showing another example of a lithium-ion secondary battery according to this embodiment. In the lithium-ion secondary battery 2 shown in FIG. 2, the same components as those in the lithium-ion secondary battery 1 shown in FIG. 1 are denoted by the same reference numerals. The lithium-ion secondary battery 2 shown in FIG. 2 has a partition wall layer 17 between the positive electrode 10 and the negative electrode 12, the partition wall layer 17 including a first partition wall layer 14 and a second partition wall layer 15. The first partition wall layer 14 is a partition wall layer including a nonaqueous solid electrolyte A and is the same as the partition wall layer 14 shown in FIG. 1. The second partition wall layer 15 is a partition wall layer including a nonaqueous solid electrolyte B having a different component from the nonaqueous solid electrolyte A.

[0070] The second partition wall layer 15 can be obtained, for example, by applying a precursor solution of the nonaqueous solid electrolyte B to a porous sheet such as a separator and drying the applied solution. The precursor solution of the nonaqueous solid electrolyte B can be the precursor solution described above for the nonaqueous electrolyte 18. Specific examples of the porous sheet include a microporous thin film, a woven fabric, a nonwoven fabric, and the like. Examples of materials for the porous sheet include olefin-based resins such as polyethylene and polypropylene, resins such as polyamide, polyamideimide, and cellulose, glass such as borosilicate glass, silica, alumina, and titania, and ceramics. The porous sheet may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, the porous sheet may be a laminate including a polyethylene layer and a polypropylene layer, or a porous sheet having a material such as an aramid-based resin or ceramic coated on its surface.

[0071] The matrix polymer in the precursor solution of the nonaqueous solid electrolyte B, i.e., the matrix polymer constituting the nonaqueous solid electrolyte B, preferably contains a fluorine-based matrix polymer, and more preferably contains polyvinylidene fluoride (PVDF), in order to suppress water permeability in the second partition layer 15, for example.

[0072] The nonaqueous solid electrolyte B contains an organic solvent. The organic solvent contained in the nonaqueous solid electrolyte B can be any of those exemplified for the nonaqueous electrolyte 18 described above. For example, it is preferable that the nonaqueous solid electrolyte B contains a cyclic organic solvent such as a cyclic carbonate, in order to suppress a decrease in lithium ion conductivity. The cyclic organic solvent is contained in an amount of preferably 30% by volume or more, more preferably 50% by volume or more, and even more preferably 80% by volume or more, based on the total volume of the organic solvents in the nonaqueous solid electrolyte B.

[0073] 2, the first partition wall layer 14 containing the nonaqueous solid electrolyte A is disposed on the positive electrode 10 side, and the second partition wall layer 15 containing the nonaqueous solid electrolyte B is disposed on the negative electrode 12 side. The arrangement of the partition walls is not limited thereto, and the first partition wall layer 14 containing the nonaqueous solid electrolyte A may be disposed on the negative electrode 12 side, and the second partition wall layer 15 containing the nonaqueous solid electrolyte B may be disposed on the positive electrode 10 side.

[0074] The thickness of the first partition wall layer 14 may be, for example, in the range of 10 μm to 50 μm, or in the range of 15 μm to 30 μm. The thickness of the second partition wall layer 15 may be, for example, in the range of 10 μm to 50 μm, or in the range of 15 μm to 30 μm. If the thicknesses of the first partition wall layer 14 and the second partition wall layer 15 are too thick, for example, the battery resistance may increase and the battery performance may deteriorate. If the thicknesses of the first partition wall layer 14 and the second partition wall layer 15 are too thin, for example, the mechanical strength may deteriorate.

[0075] The partition wall layer 17, which is a laminate of a first partition wall layer 14 containing a nonaqueous solid electrolyte A and a second partition wall layer 15 containing a nonaqueous solid electrolyte B, can be produced, for example, by immersing a polymer skeleton produced by a phase inversion method in a nonaqueous electrolytic solution to produce a nonaqueous solid electrolyte A, and then placing the nonaqueous solid electrolyte A on the nonaqueous solid electrolyte B and heating (drying). Alternatively, a single partition wall layer in which the nonaqueous solid electrolytes A and B are integrated can be produced, for example, by adding a precursor solution of the nonaqueous solid electrolyte B to the nonaqueous electrolytic solution when producing the nonaqueous solid electrolyte A by immersing a polymer skeleton produced by a phase inversion method in a nonaqueous electrolytic solution, or by immersing the produced nonaqueous solid electrolyte A in a precursor solution of the nonaqueous solid electrolyte B.

[0076] Examples of the battery case 24 include a metal case, a resin case, and a laminate film case. Examples of materials for the metal case include nickel, iron, and stainless steel. Examples of materials for the resin case include polyethylene and polypropylene. Examples of the laminate film include a multilayer film in which stainless steel foil is coated with a resin film. Examples of materials for the resin film include polypropylene, polyethylene, nylon, and polyethylene terephthalate.

[0077] The lithium ion secondary battery of this embodiment can be used in various forms such as a square type, a cylindrical type, a flat type, a thin type, a coin type, and a laminate type. [Example]

[0078] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0079] Example 1 [Negative electrode] Graphite as the negative electrode active material, SBR as the binder, and CMC as the thickener were mixed in a solids mass ratio of 98:1:1, and water was added to prepare a negative electrode composite slurry. Next, the negative electrode composite slurry was applied to a negative electrode current collector made of copper foil, the coating was dried, and then rolled with a rolling roller. The negative electrode was then cut to a predetermined electrode size to obtain a negative electrode. The application amount of the negative electrode composite slurry and the packing density of the negative electrode composite layer were 128 g / m, respectively. 2 , 1.7gcm -3 It was.

[0080] [Positive electrode] LiNi as a positive electrode active material 0.82 Co 0.15 Al 0.03O2, carbon black as a conductive material, and PVDF as a binder were mixed in a mass ratio of 98:1:1, and N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode composite slurry. Next, the positive electrode composite slurry was applied to a positive electrode current collector made of Ti foil, the coating was dried, and then rolled with a rolling roller. The positive electrode was then cut to a predetermined electrode size to obtain a positive electrode. The application amount of the positive electrode composite slurry and the packing density of the positive electrode composite layer were 234 g / cm, respectively. 2 , 3.7gcm -3 It was.

[0081] [Non-aqueous liquid electrolyte] A non-aqueous liquid electrolyte was prepared by dissolving 1M LiTFSI in a mixed solution of fluoroethylene carbonate (FEC) and methyl 3,3,3-trifluoropropionate (FMP) in a volume ratio of 30:70.

[0082] [Aqueous liquid electrolyte] LiTFSI, LiBETI, and water were mixed in a molar ratio of 0.7:0.3:2.0 to prepare an aqueous liquid electrolyte in which LiTFSI and LiBETI were dissolved in water.

[0083] [First partition layer] A solution of 10% by mass of acrylonitrile-methyl methacrylate copolymer, a matrix polymer, was added to a DMF (dimethylformamide) solvent and stirred at 85°C until the matrix polymer was completely dissolved. This solution was applied to a glass plate to a thickness of 25 μm, and water was added dropwise to solidify the matrix polymer, yielding a polymer skeleton with a porous structure. The polymer skeleton was peeled from the glass plate and immersed in water for 10 minutes, and then dried overnight in a vacuum oven at 100°C.

[0084] A nonaqueous electrolyte solution was prepared by dissolving 1 M LiTFSI in a mixed solvent of fluoroethylene carbonate (FEC) and methyl 3,3,3-trifluoropropionate (FMP) in a volume ratio of 90:10. The dried polymer skeleton was immersed in the nonaqueous electrolyte solution for 60 seconds. The excess liquid on the polymer skeleton was then wiped off, and the polymer skeleton was dried in a dryer at 80°C for 20 minutes to obtain a gel-like nonaqueous solid electrolyte membrane. This was used as the first partition wall layer.

[0085] [Second partition layer] An electrolyte solution was prepared by dissolving 1 M LiTFSI in a mixed solution of fluoroethylene carbonate (FEC) and methyl 3,3,3-trifluoropropionate (FMP) in a volume ratio of 9:1. Next, 4 mass% polymethyl methacrylate (PMMA) and 8 mass% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) were prepared and dissolved in a solvent containing 10 times the amount of THF (tetrahydrofuran) and 10 times the amount of acetone relative to the amount of PMMA. The electrolyte solution was then mixed with this solution to prepare a precursor solution for a nonaqueous solid electrolyte. A porous sheet was then immersed in the precursor solution and dried at 60°C for 1 hour to obtain a porous sheet coated with the nonaqueous solid electrolyte. This was used as the second partition layer.

[0086] [Test cell] The negative electrode with the negative electrode lead attached was immersed in a non-aqueous liquid electrolyte to obtain a negative electrode impregnated with the non-aqueous liquid electrolyte. The positive electrode with the positive electrode lead attached was immersed in an aqueous liquid electrolyte to obtain a positive electrode impregnated with the aqueous liquid electrolyte. The electrode assembly with the first partition wall layer disposed between the negative electrode and the positive electrode was housed in a battery case as shown in FIG. 1 to prepare a test cell.

[0087] <Example 2> A test cell was fabricated in the same manner as in Example 1, except that an electrode assembly was used in which the positive electrode side served as the first partition wall layer and the negative electrode side served as the second partition wall layer between a negative electrode impregnated with a nonaqueous liquid electrolyte and a positive electrode impregnated with an aqueous liquid electrolyte.

[0088] <Comparative Example 1> A test cell was produced in the same manner as in Example 1, except that an electrode assembly without a partition wall layer was used between a negative electrode impregnated with a nonaqueous liquid electrolyte and a positive electrode impregnated with an aqueous liquid electrolyte.

[0089] <Comparative Example 2> A test cell was produced in the same manner as in Example 1, except that an electrode assembly was used in which a second partition wall layer was disposed between a negative electrode impregnated with a nonaqueous liquid electrolyte and a positive electrode impregnated with an aqueous liquid electrolyte.

[0090] [Charge / discharge cycle test] The test cells of each example and comparative example were charged at a constant current of 0.05 C to 4.2 V and then rested for 20 minutes. Thereafter, they were discharged at a constant current of 0.05 C to 2.5 V and then rested for 20 minutes. This charge / discharge cycle was repeated 10 times, and the capacity retention rate was calculated using the following formula. Capacity retention rate (%) = (discharge capacity at 10th cycle ÷ discharge capacity at 1st cycle) × 100

[0091] Table 1 summarizes the discharge capacity at the 10th cycle for each example and comparative example, and the capacity retention rate calculated by the above formula. Note that the discharge capacity shown in Table 1 is shown as a relative value, with the discharge capacity of Example 2 set as 100 (reference), and the discharge capacities of the other examples and comparative examples. Also, a higher value of the capacity retention rate shown in Table 1 indicates that the capacity decrease due to charge / discharge cycles is more suppressed.

[0092] [Table 1]

[0093] Examples 1 and 2 exhibited higher values ​​for both the discharge capacity and the capacity retention rate than Comparative Examples 1 and 2. From these results, it can be said that Examples 1 and 2, in which a nonaqueous solid electrolyte containing an acrylonitrile-methyl methacrylate copolymer was used as the partition layer, were able to suppress the capacity decrease that occurs with the charge-discharge cycles of a lithium ion secondary battery that uses an aqueous electrolyte. [Explanation of symbols]

[0094] 1, 2 Lithium ion secondary battery, 10 Positive electrode, 12 Negative electrode, 14 Partition wall layer or first partition wall layer, 15 Second partition wall layer, 16 Aqueous electrolyte, 17 Partition wall layer, 18 Non-aqueous electrolyte, 20 Positive electrode lead, 22 Negative electrode lead, 24 Battery case, 26 Positive electrode current collector, 28 Positive electrode composite layer, 30 Negative electrode current collector, 32 Negative electrode composite layer, 34 Positive electrode active material, 36 Negative electrode active material.

Claims

1. a negative electrode, a positive electrode, a non-aqueous electrolyte containing a lithium salt, an aqueous electrolyte containing a lithium salt, and a partition wall layer disposed between the negative electrode and the positive electrode; the aqueous electrolyte is a liquid electrolyte containing the lithium salt and an aqueous solvent, or a solid electrolyte in which the lithium salt, an aqueous solvent, and a matrix polymer are composited; the aqueous electrolyte is in contact with only the positive electrode of the negative electrode and the positive electrode; the nonaqueous electrolyte is in contact with at least the negative electrode of the negative electrode and the positive electrode; the partition layer contains a nonaqueous solid electrolyte A in which a matrix polymer and a nonaqueous electrolyte solution are composited, The lithium ion secondary battery, wherein the matrix polymer comprises a copolymer of acrylonitrile with at least one of methyl methacrylate, methyl acrylate, and vinyl acetate.

2. 2. The lithium ion secondary battery according to claim 1, wherein the matrix polymer is an acrylonitrile-methyl methacrylate copolymer.

3. The lithium ion secondary battery according to claim 1 , wherein the partition layer contains a non-aqueous solid electrolyte B having a component different from that of the non-aqueous solid electrolyte A.

4. 4. The lithium ion secondary battery according to claim 3, wherein the partition wall layer has a laminated structure in which a first partition wall layer containing the nonaqueous solid electrolyte A and a second partition wall layer containing the nonaqueous solid electrolyte B are stacked.

5. 5. The lithium ion secondary battery according to claim 3, wherein the non-aqueous solid electrolyte B contains a fluorine-based matrix polymer.

6. 6. The lithium ion secondary battery according to claim 5, wherein the fluorine-based matrix polymer comprises polyvinylidene fluoride (PVDF).

7. 7. The lithium ion secondary battery according to claim 5, wherein the nonaqueous solid electrolyte B contains an organic solvent including a cyclic organic solvent, and the cyclic organic solvent accounts for 50% by volume or more of the total volume of the organic solvent.

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